Zone‑3 Hepatocyte Senescence Driven by Mitochondrial Iron‑Lipid Crosstalk Fuels Systemic Metabolic Decline in MASLD

Hypothesis: In MASLD, zone‑3 hepatocytes accumulate labile iron due to impaired ferroportin export, which amplifies lipid peroxidation and triggers ferroptotic senescence. This senescent phenotype spreads via extracellular vesicle‑mediated transfer of oxidized lipids and mitochondrial DNA, causing paracrine aging in distant organs such as pancreas, kidney and heart, thereby linking hepatic zonation to systemic metabolic dysfunction.

Mechanistic basis

• Hypoxia‑iron axis: Low O2 in pericentral zones stabilizes HIF‑1α, which upregulates transferrin receptor (TFRC) and downregulates ferroportin (FPN1), increasing intracellular labile iron [https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2017.0443].
• Lipid overload: Reduced fatty acid oxidation and impaired PNPLA3‑mediated lipolysis cause lipid droplet accumulation, providing substrates for peroxidation [https://pmc.ncbi.nlm.nih.gov/articles/PMC8773141/].
• Ferroptosis trigger: Labile iron catalyzes Fenton reactions, generating lipid ROS that overwhelm GPX4 capacity, pushing hepatocytes toward ferroptotic damage [https://pmc.ncbi.nlm.nih.gov/articles/PMC12810195/].
• Senescence diversion: Sublethal ferroptotic stress activates p53‑p21 and DNA damage pathways, establishing the Aging Hepatocyte Gene Signature (AHGS) and a senescence‑associated secretory phenotype (SASP) [https://pmc.ncbi.nlm.nih.gov/articles/PMC12810195/].
• Paracrine spread: Senescent hepatocytes release extracellular vesicles enriched in oxidized phospholipids and mitochondrial DNA. Upon uptake by extra‑hepatic cells, these cargoes activate cGAS‑STING and NF‑κB signaling, propagating senescence and metabolic dysfunction to pancreas, kidney and heart [https://pmc.ncbi.nlm.nih.gov/articles/PMC12810195/].

Testable predictions

1. Iron imaging: Quantify labile iron in zone‑3 versus zone‑1 hepatocytes using calcein‑AM quenching in human MASLD biopsies; zone‑3 will show a ≥2‑fold higher labile iron pool [https://pmc.ncbi.nlm.nih.gov/articles/PMC2346454/].
2. Ferroportin manipulation: Genetic overexpression of ferroportin specifically in zone‑3 hepatocytes (using AAV8‑HGF promoter) will reduce AHGS incidence from ~44% to <15% in aged MASH mice, without altering overall iron load [https://pmc.ncbi.nlm.nih.gov/articles/PMC12810195/].
3. EV transfer: Isolate EVs from senescent zone‑3 hepatocytes and inject them into healthy mice; recipient pancreas, kidney and heart will exhibit increased p21^WAF1^ expression and impaired glucose tolerance within two weeks [https://pmc.ncbi.nlm.nih.gov/articles/PMC12810195/].
4. Therapeutic window: Combined treatment with a ferroptosis inhibitor (Fer‑1) and an HIF‑2α antagonist will synergistically lower zone‑3 AHGS and improve systemic insulin sensitivity more than either agent alone in aged MASH mice [https://pmc.ncbi.nlm.nih.gov/articles/PMC12810195/].

Falsifiability

If zone‑3 hepatocytes do not display elevated labile iron relative to zone‑1, or if ferroportin overexpression fails to diminish AHGS despite reducing iron, the hypothesis is refuted. Likewise, lack of senescence‑inducing activity in hepatocyte‑derived EVs would falsify the paracrine aging mechanism.

This framework integrates zonation‑specific iron handling, lipid peroxidation, and vesicle‑mediated senescence to explain how a localized hepatic lesion drives multi‑organ metabolic decline in MASLD.